1. Field of the Invention
The present invention relates to a seat back framework of a vehicle or automotive seat, and in particular to a structure of seat back frame which includes a lateral frame section and a connecting bracket fixed to the lower end portion of that lateral frame section, wherein the connecting bracket is adapted for operative connection, via a reclining device or the like, with the side of a seat cushion frame.
2. Description of Prior Art
As shown, for instance, in FIG. 1, most of conventional seat back frameworks, designated by (BF), are generally of a rectangular configuration on the whole. Some of the seat back frameworks of this sort, as in the FIG. 1, comprise an upper frame section (18A), a lower frame section (18B) and a pair of lateral plate frame sections (14A) (14A) fixedly connected between the upper and lower frame sections (18A) (18B). A plurality of springs (15) are extended between the two lateral plate frame sections (14A) for the purpose of resiliently supporting the back of a person resting on the seat back frame (BF). While not shown, an elastic upholstery is attached over this seat back frame (BF) to produce a seat back, one of the constituent elements of a vehicle or automotive seat.
As illustrated, the seat back frame (BF) is rotatably connected via a pair of reclining devices (11) (11) or the like with a seat cushion frame (CF) such as to be selectively inclinable in the forward and backward directions with respect thereto. In particular, the lower end portions (14Ae) respectively of the pair of lateral plate frame sections (14A) are operatively connected with such two reclining devices (11) respectively.
In the foregoing construction of seat back frame (BF), however, a load is intensively applied to those lower end portions (14Ae) of lateral frame sections (14A) from a person resting on the seat back frame (BF) thus requiring a proper robustness of those particular portions (14Ae) to withstand a corresponding stress caused therein by the load. Particularly, in a collision case, as an excessive great load is intensively exerted upon the end portions (14Ae), a further increased rigidity is required therein to resist the load.
Hitherto, such problem has been solved by increasing the thickness of the lateral plate frame sections (14A), but it raises such problem that those particular frame sections (14A) themselves weigh greater unexpectedly, resulting in an inevitable cost increase, an unfavorable factor in practical assembly of seat cushion frame. Another attempt to solve the problem has been proposed by cutting off the lower portion of the lateral frame section (14A) and instead connecting a thickened rigid bracket member to the thus-cut lower portion of lateral frame section, to provide a robust structure of lateral frame section that avoids increase in weight and assembling costs of the seat cushion frame. In such conventionally proposed countermeasure, the thickened rigid bracket member is normally in a generally horizontal connection relation with the cut-off portion of lateral frame section. In other words, as both edges of the bracket member and lateral frame section are formed straight and sheer normally, the connected and juxtaposed areas between them naturally assumes a generally horizontal line in relation to the vertical line of the lateral frame section. Indeed, this provision of rigid bracket member adds to an effective reinforcement of the lower end portion of lateral frame section in question. But, to further amplify the reinforcement, one will be forced to consider increasing the length of thickened bracket member while further cutting off the remaining portion of lateral frame section itself, which will however unnecessarily expand an reinforcement area in the lateral frame section beyond its lower end portion that actually requires reinforcement as it is a main area to receive the load intensively.
This might again encounter the same high-cost and high-weight problem as above.
In view of the above-stated shortcomings, it is a primary purpose of the present invention to provide an improved seat back frame structure for use in a seat back of a vehicle seat, which insures to attain a reduction of its weight while maintaining a required reinforcement of the lateral frame section thereof.
In order to achieve such purpose, a structure of the seat back frame in the present invention is basically comprised of:
a reduced lower area defined in each of a pair of lateral frame sections of the seat back frame, the reduced lower area being defined by reducing a portion of each of a pair of lateral frame sections of the seat back frame which corresponds to lower end portion thereof, and having a lower edge; and
a connecting bracket means having a slant edge so formed in one end thereof as to extend in a downwardly inclined manner as it proceeds toward one side of the seat back frame which is to face a forward side of the vehicle seat;
wherein the connecting bracket means and reduced lower area of each of the two lateral frame sections are juxtaposed and fixedly connected together such that a predetermined juxtaposition area is defined between those lower and slant edges in a direction from another side, which is to face a rearward side of the vehicle seat, toward the aforementioned one side.
Accordingly, dynamically stated, the upper end portion of the connecting bracket means, by the reason that it is formed slant, becomes larger in rigidity as it proceeds in the direction from the forward side to the rearward side of vehicle seat, which means that the rigidity becomes gradually lager in that direction. This gentle gradient of rigidity works to gradually disperse and reduce a load being applied from the forward side to the lateral frame section, whereby any immediate transmission of the load through the lateral frame section is blocked, and at the same time, dispersion of the load becomes larger along the slant edge, thereby positively preventing the load""s intensive exertion on one localized point in the lateral frame section. At the same time, such partial increase of connecting bracket means, only at a point where a compressive load applies, limits its rigidity precisely thereto and thus eliminates any unnecessary increase of its weight. Therefore, both light weight and increased rigidity aspects can be achieved in the seal back frame.
Preferably, the lower end portion of the lateral frame section may also be formed with a slant edge as likewise in the slant edge of connecting bracket means, so that a slant juxtaposition area is defined in a downwardly inclined way in the direction from the rearward side to the forward side.
Preferably, an upwardly protruded portion may be formed in the rearward-side end area of the slant edge of connecting bracket means and disposed within a predetermined area of the lateral frame section to which an upper frame section of the seat back frame is fixedly connected.